Moving filter logic to RPC layer for member filtering. This prevents two
antipatterns:

- Every client implementing the same filtering
- Always fetching all members and reducing later
Only construct a Member struct if it is to be added to the result
Using regular expressions to compare tags. We are now adding line-start and
line-end characters around the pattern, and splatting stars (*) into dot-start
(.*) so that the regex will act similar to how one would expect from a command
line tool.

It is not likely that someone would pass something like
-tag role=^(app|cache)-[0-9]+$ on the command line. More common patterns would
be things like -tag role=*web , or -tag active=* (to match any with the tag).

Furthermore, the line-start and line-end injection is necessary, as one would
not expect something like -tag role=a to include nodes with a tag of role=cache.
In our previous implementation, this would still match due to the open-endedness
of the regular expression, and the MatchString() method. If a user really wants
to match all nodes with a tag containing the letter a, they would more likely do
something like -tag role=*a*
Added simple filtering on status. Since there are only a few known
statuses, and likely only a few more (if any) will be added, we probably
don't need to regex match them, and a simple equality test should do.
Make tests pass. Added back -role filter, which just inserts another tag, which goes through the normal tags filtering.
website: updated members rpc call information
agent: filter status by regexp
client: test rpc client member tag filtering
gofmt
agent: update regex patterns for filtering
agent: support members and filtered-members commands to preserve backward compatibility
client: add filteredMembers command
renamed filteredMembers -> membersFiltered
agent: fix tests for membersFiltered command
website: update rpc documentation for members-filtered
agent: rename membersRequest -> membersFilteredRequest
Merge branch 'master' into filter_via_rpc
client: cleaned up tests for MembersFiltered
client: more MembersFiltered test cleanup
client: finished test cleanup and removed an unnecessary double-call to client.UpdateTags.