Add SENTINEL INFO-CACHE [masters...]

Sentinel queries the INFO from every master and from every replica of
every master.

We can cache the INFO results in Sentinel so Sentinel can be a single
place to quickly get all INFO output for an entire Sentinel monitoring
group.

This commit gives us SENTINEL INFO-CACHE in two forms:
  - SENTINEL INFO-CACHE — returns all masters and all replicas
  - SENTINEL INFO-CACHE master0 master1 ... masterN — vararg specify masters

Results are returned as a multibulk reply with two top-level entries
for each master.  The first entry for each master is the name of the master.
The second entry is a nested multibulk reply with the contents of INFO,
first for the master, then an additional entry for each of the
replicas.
Update sds.c

in the case (all chars of the string s found in 'cset' ),
line[573] will no more do the same thing line[572] did.
this will be more faster especially in the case that the string s is very long and all chars of string s found in 'cset'
sds.c: more tests for sdstrim().
test-sds target in Makefile to run sds.c tests.
Merge pull request #2203 from Brochen/unstable

Update sds.c
Merge branch 'unstable' of github.com:/antirez/redis into unstable
Merge pull request #2148 from mattsta/feature/sentinel/info-cache

Add SENTINEL INFO-CACHE [masters...]