Fix DD DLB state issue

Fix DD DLB state issue

The introduction of DLB locking for PME load balancing added another
DLB state, which was stored in a third variable. These variables
were not always all properly checked. Simplified the code by merging
these three state variables into one. In added there was a fourth
variable (bGridJump) is gmx_domdec_t, this is replaced by calls to
a functions returning is DLB is on.

Refs #1760.

Change-Id: I80d499149e4e5bfd689e76208384a8ba61e2842a