Add timeout to mnesia calls in ns_mnesia:ensure_table
Add timeout to mnesia calls in ns_mnesia:ensure_table

Schema operations can sometimes hang when they happen right around the
time we take a backup.

Change-Id: Ia978947aafb63ef133f10c02abb976be88c8f692
Reviewed-on: http://review.membase.org/4566
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

daverigby/ns_server,membase/ns_server,vzasade/ns_server,nimishzynga/ns_server,membase/ns_server,daverigby/ns_server,ceejatec/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,ceejatec/ns_server,membase/ns_server,nimishzynga/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,membase/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,membase/ns_server,vzasade/ns_server,vzasade/ns_server,vzasade/ns_server,daverigby/ns_server,nimishzynga/ns_server,membase/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,mschoch/ns_server,nimishzynga/ns_server