PWX-27551-pt1: SSL fixes (kvdb)

[zoxpx]

• adding IsTLSEnabled() into etcd-common
  • IsTLSEnabled() returns TRUE if options[TransportScheme]=https, or if client SSL cert was provided
• the EtcD endpoint URLs will be prefixed either with http:// or https://

Signed-off-by: Zoran Rajic zrajic@purestorage.com

What this PR does / why we need it: ISSUE:

• without this fix, the kvdb library always constructs non-SSL endpoints -- which is wrong if kvdb is running in SSL-mode

FIX:

• the caller can explicitly set options[TransportScheme]=https to enable SSL support, also
• if caller supplied end-client SSL certs, we'll also automatically enable SSL support

Which issue(s) this PR fixes (optional) Closes # PWX-27551 (part 1)

Special notes for your reviewer: This fix will be combined with the "part 2" fix in the porx code.

[zoxpx]

Thank you Grant -- merging this change (and will vendor it in).