NEXUS-6219: Duplicate processing of reposes

When bulk operation happened (as task om "all" repositories)
or user right-clicked on UI over some group that contained
groups-of-groups (or just same repo was resolved multiple times)
the some repositories were processed multiple times.

Affected actions:

Hosted repositories:
* expireCaches
* expireNotFoundCaches
* evictUnusedItems
* recreateAttributes

Proxy repositories:
* expireProxyCaches

Maven repositories
* recreateMavenMetadata
NEXUS-6219: Pass over the filter

It got lost in the method.
NEXUS-6219: Minor changes, redundant checks
Upgrade HC3 to 4.3.2
Updated UT

As it tests discovery error message, that comes from
HC4 (as it tries to connect to something not existant)
and wording there changed. Laxed the assertion
Merge pull request #320 from sonatype/hc4-432

Upgrade HC4 to latest (4.3.2)
NEXUS-6219: Consolidate logging

Making them similar to other 3 operations.
Merge pull request #319 from sonatype/NEXUS-6219-duplicate-processing

NEXUS-6219: Duplicate processing of reposes
Making Server response header consistent.

noticed while testing, that static resources
sometime respond with Nexus as Server, and sometimes
as Jetty.

It turned out, that only GETs would have proper
Server header set. Applying same solution as present
in ContentServlet.

Ultimately, this should be set by some filter, and not
have to fiddle with these "standard" headers (common
to all responses from server) on per-servlet basis.
Fixing ugly NPE/log pollition

If someone (by browser or curl) accesses the ErrorPageServlet.
As this request would be "unexpected", an NPE happened in it,
that caused nasty stack trace in log, and then ErrorFilter
would kick in, spitting the stack trace again (double NPE
in logs).

It was simply matter of Integer/int autoboxing and casting.
Now a simple check is added, to detect when page is
accessed externally and providing somewhat sensible
404 not found response instead of 500 Server Error
(and stack trace in log).
Added filter for "common" headers

Removed littered use of same code from multiple places.
Now whole Nexus responds with proper Server header, unlike
before.
Revert "Merge pull request #320 from sonatype/hc4-432"

This reverts commit 74e0ecea8917df5c71f8b63e51ea745f333b4c65, reversing
changes made to 1855357e1f6fc5a3986b431fe4a5d526bca24e83.
Merge remote-tracking branch 'origin/master' into rapture
Mask UI in case of server disconnected