Fix acquisition loop to works correctly with base 7.0.5

The change introduced by this commit https://code.launchpad.net/~dirk.zimoch/epics-base/+git/epics-base/+merge/394327 on epics base changes the way the mutex works. Due to that the acquisition loop when at 14Hz got in a wrong state: When the state machine is going to RESET or INIT the acquisition loop tries to arm the device, but on this situation the device cannot be armed and goes to error state.

It is not clear which change on mutex changes this behavior, but it was possible to fix the issue checking on loop acquisition on 2 different points if the state machine was different then ON (the only state which the acquisition should happen).