fs_mgr_priv: Extend fs wait timeout to 20 seconds

In practice 5 seconds is too short to wait for a disk device node to
show up if the disk is USB; 20 seconds is a much more comfortable
window.

Change-Id: Iaf2c1f46b41a44fc1240d52d8498ca9cb639ea80
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
Merge "fs_mgr_priv: Extend fs wait timeout to 20 seconds"
Merge branch 'master' of https://android.googlesource.com/platform/system/core