Use __thread instead of pthread_get_specific in logging code

Convert the thread-specific data to thread local storage,
so we eliminate the expensive pthread_[get|set]specific code.

This also eliminates the need for the emergency_context because
we can static initialize the thread local storage.

Also, trim maximum thread name, and make it static so we aren't
dynamically allocating it.

Signed-off-by: Poornima Gupte <poornima.gupte@in.ibm.com>
Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
Trim some long thread names to be 15 chars or less

The new logging code limits thread names to 15 chars or less so make
all these threads conform.

I did not do FSAL_PT to avoid collisions with checkpatch work there.

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>