EtcdConfig: Fix infinite timeout bug, and reduce timeout

EtcdConfig: Fix infinite timeout bug, and reduce timeout

removeServer() returns the modified array, rather than passing by
reference, so you have to use the return value to avoid an infinite loop
when a server is down.

Tune the timeout downwards, to 2s. With three servers in the SRV pool,
if they are all unreachable, this will mean an overall request time of
6s, which is conveniently less than the APC lock time and the cache
TTL (9-10s). If the APC lock time is significantly shorter than the time
it takes to do the HTTP requests, then additional threads join in
waiting for the server. This could have stability consequences if the
maximum HHVM worker count is exceeded.

Change-Id: I3176aa41b8833c0ba0b668859e59911cd4392250