[Travis+Jenkins] startup fails, crash in mem3_shards:get_update_seq

[wohali]

Expected Behavior

When the build process hits make javascript, dev/run should succeed in starting up a 1-node instance.

Current Behavior

Occasionally, as in this log, startup fails. We don't know exactly why in this case, as the logfile uploader was not yet present on the 2.1.x branch.

[EDIT] A subsequent failure turned up the real failure here (2.1.x branch, Ubuntu 12.04, Erlang 18.3). Logfile: https://paste.apache.org/IXst

CRASH REPORT Process  (<0.297.0>) with 0 neighbors exited with reason: no match of right hand value file_exists at mem3_shards:get_update_seq/0(line:318) <= mem3_shards:init/1(line:206)

[wohali]

Fix from master cherry-picked: 9875e8b