NEXUS-6164: Expose SSL cert check lax options

ConnectionInfo now carries flags about relaxing the
X509 hostname check and SSL certificate check,
thus it's possible to make Nexus client accept
self signed certificates and certificates with
different X509 hostname that the name of the
host it connects to.

Also, client used default connection manager
(usable in single thread environment), but this
time it's set explicitly and made to honor
JSSE system properties, allow greater customization.
Merge remote-tracking branch 'origin/master' into NEXUS-6164-lax-client-ssl
NEXUS-6164: Renames and tweaks
Deprecate Check class

in favor of Guava
Undo method check made in 6189ef698a5a37258e93dbfb5367dfa7baeaa216

To keep it still simple, but deprecation still stands.
NEXUS-6164: Fixed UT incomplete mock
Merge pull request #281 from sonatype/NEXUS-6164-lax-client-ssl

NEXUS-6164: Expose SSL cert check lax options