NEXUS-6155: Connection constraint and error handling

Upped connection version constraint to 2.7+.
Removed the error handling, as it was hiding the cause.
Nexus client does good job at converting and explaining error
cause, so using the message if possible.
NEXUS-6155: Comment
NEXUS-6164: lax client ssl checks

Exposed settings using same properties as wagon uses.
Merge remote-tracking branch 'origin/master' into NEXUS-6164-lax-client-ssl
NEXUS-6164: Applied renames and tweaks
Merge pull request #60 from sonatype/NEXUS-6164-lax-client-ssl

NEXUS-6164: lax client ssl checks
Merge pull request #59 from sonatype/NEXUS-6155-m2settings-constraints-and-error

NEXUS-6155: Connection constraint and error handling
Merge remote-tracking branch 'origin/master' into NEXUS-6094-be-aware-of-build-failures

Conflicts:
	staging/maven-plugin/src/main/java/org/sonatype/nexus/maven/staging/AbstractStagingMojo.java