Handle the error better when all the hosts are excluded using '-x' command

[mattsfuller]

On a four node cluster with master, slave1, slave2 and slave3, if I run a presto-admin command with '-x' and mention all the hosts, the error message shown to the user is not helpful at all from the user's perspective. For example:
$./prestoadmin/presto-admin connector add -x master,slave1,slave2,slave3
Deploying hive.properties connector configurations on: None
Fatal error: Needed to prompt for the target host connection string (host: None), but input would be ambiguous in parallel mode
Aborting.
$./prestoadmin/presto-admin configuration show -x master,slave1,slave2,slave3
Fatal error: Needed to prompt for the target host connection string (host: None), but input would be ambiguous in parallel mode
Aborting.
A better error message should be along the lines of: "You have chosen to exclude all the nodes for running this command, hence this operation is essentially a no-op"
I suspect that this is true for all presto-admin commands that support '-x' option, though I haven't tested it for all the commands.
The fix may not be as simple as modifying an existing error message. You may have to dig deeper to fix it.
Also opened a PR: #158
Add a negative test for presto admin commands for this scenario.