Add ability to bypass certificate authority check if, say, the https-enabled server uses a self-signed cert

[schahal]

Related to the following issue: #11

Test Results

Unit tests:

$ make test
==> Checking that code complies with gofmt requirements...
go test -i $(go list ./... |grep -v 'vendor') || exit 1
echo $(go list ./... |grep -v 'vendor') | \
	xargs -t -n4 go test  -timeout=30s -parallel=4
go test -timeout=30s -parallel=4 github.com/terraform-providers/terraform-provider-influxdb github.com/terraform-providers/terraform-provider-influxdb/influxdb 
?   	github.com/terraform-providers/terraform-provider-influxdb	[no test files]
ok  	github.com/terraform-providers/terraform-provider-influxdb/influxdb	0.006s

Acceptance test:

==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v  -timeout 120m
?   	github.com/terraform-providers/terraform-provider-influxdb	[no test files]
=== RUN   TestAccInfluxDBContiuousQuery
--- PASS: TestAccInfluxDBContiuousQuery (0.27s)
=== RUN   TestProvider
--- PASS: TestProvider (0.00s)
=== RUN   TestProvider_impl
--- PASS: TestProvider_impl (0.00s)
=== RUN   TestAccInfluxDBDatabase
--- PASS: TestAccInfluxDBDatabase (0.13s)
=== RUN   TestAccInfluxDBDatabaseWithRPs
--- PASS: TestAccInfluxDBDatabaseWithRPs (0.38s)
=== RUN   TestAccInfluxDBUser_admin
--- PASS: TestAccInfluxDBUser_admin (0.41s)
=== RUN   TestAccInfluxDBUser_grant
--- PASS: TestAccInfluxDBUser_grant (0.89s)
=== RUN   TestAccInfluxDBUser_revoke
--- PASS: TestAccInfluxDBUser_revoke (0.50s)
PASS
ok  	github.com/terraform-providers/terraform-provider-influxdb/influxdb	2.592s

Functional Tests

Setting and unsetting the environment variable

$  export INFLUXDB_SKIP_SSL_VERIFY=1
$  terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.

influxdb_database.demo-test-db-creation: Refreshing state... (ID: demo_test_tf_db)

------------------------------------------------------------------------

No changes. Infrastructure is up-to-date.

This means that Terraform did not detect any differences between your
configuration and real physical resources that exist. As a result, no
actions need to be performed.
$  export INFLUXDB_SKIP_SSL_VERIFY=0
$  terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.


Error: Error refreshing state: 1 error(s) occurred:

* provider.influxdb: error pinging server: Get https:/<REDACTED>:8443/ping: x509: certificate signed by unknown authority


$  unset INFLUXDB_SKIP_SSL_VERIFY
$  terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.


Error: Error refreshing state: 1 error(s) occurred:

* provider.influxdb: error pinging server: Get https://<REDACTED>:8443/ping: x509: certificate signed by unknown authority

Updating config to include skip_ssl_verify

provider “influxdb” {
 url      = “https://<REDACTED>:8443”
 username = “admin”
 skip_ssl_verify = true
}

$ terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.


------------------------------------------------------------------------

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
 + create
...

[schahal]

@radeksimko , @katbyte , @catsby : looking for a maintainer (or write-access member) of this repo to review this PR (and hopefully merge) so we can use the OSS version for an https-enabled InfluxDB with self-signed cert (rather than the patched one :) ) Thanks for your time!

[sidgod]

@schahal Apologies for the delay, will finish reviewing this in next 2-3 days!

[sidgod]

Change looks good!