NEXUS-6179: Fix redirect strategy index page detection

Clearing up what is the code expectation, how we detect is
redirect leading to an index page or not (by linking a Google
blog entry explaining it).

Improving code to be "schema switch" or "hostname switch"
resilient, by basically only assuming that remote is properly
set up and index pages will lead to URLs having paths
with trailing slash.

Also, using parsed URIs for this, to circumvent any possible
query parameter in redirect response (something old code
did not account for).
NEXUS-6179: Control strategy logic kick in

The redirect strategy should kick in only when Nexus goes
remotely to grab a content (RRS#retrieveItem basically).

In every other case, it should behave in "usual" way, as
there are very exotic setups out there, like the one
described in issue NEXUS-5744
NEXUS-6179: Simplified code

Reusing as much as possible from parent class
of our RedirectStrategy. Also, the fallback
to "naive" method was wrong, as ProtocolException
should be thrown in that case, that is now
handled by createLocationURI method from
parent.
NEXUS-6179: Javadoc changes
Merge pull request #287 from sonatype/NEXUS-6179-redirect-strategy

[2.7] NEXUS-6179: Fix redirect strategy index page detection