Simplify SCIOND client API implementation

[scrye]

Specifically:

• remove the SCIOND client API caching layer; it had a low impact on
  performance for the code complexity it added;
• applications were using the "reconnecting" implementation of the
  client API; now that is the only available implementation;
• migrate to serrors;
• remove locking since now calls are independent;

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This change is 

[lukedirtwalker]

Reviewed 3 of 3 files at r1.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @scrye)

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go/lib/sciond/sciond.go, line 48 at r1 (raw file):

U

usually we start error messages with lower case. https://github.com/golang/go/wiki/CodeReviewComments#error-strings

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go/lib/sciond/sciond.go, line 82 at r1 (raw file):

_ bool

why not just remove it already?

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go/lib/sciond/sciond.go, line 141 at r1 (raw file):

	if initialCheckTimeout != 0 {
		deadline := time.Now().Add(initialCheckTimeout)
		deadlineCtx, cancelF := context.WithDeadline(context.Background(), deadline)

wait why not just use context.WithTimeout since you get a timeout?

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go/lib/sciond/sciond.go, line 148 at r1 (raw file):

	dispatcher, err := c.ctxAwareConnect(ctx)
	if err != nil {
		return serrors.WrapStr("Unable to connect to SCIOND", err)

ditto lower case

[scrye]

Reviewable status: 2 of 7 files reviewed, 4 unresolved discussions (waiting on @lukedirtwalker and @scrye)

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go/lib/sciond/sciond.go, line 48 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

U

usually we start error messages with lower case. https://github.com/golang/go/wiki/CodeReviewComments#error-strings

Done.

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go/lib/sciond/sciond.go, line 82 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

_ bool

why not just remove it already?

Forgot about it. Fixed.

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go/lib/sciond/sciond.go, line 141 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

wait why not just use context.WithTimeout since you get a timeout?

Ah, it used to be lower in the function after some of the timeout was used up already, so an absolute deadline was simpler.

Now it no longer makes sense; fixed.

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go/lib/sciond/sciond.go, line 148 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

ditto lower case

Done.

[lukedirtwalker]

Reviewed 5 of 5 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved