testsuite: Fix timeout issues during print of vla-arrays.

Printing and resolving of dynamic array's causes sporadic timeout issues on loaded systems.

2016-03-02  Bernhard Heckel  <bernhard.heckel@intel.com>

gdb/testsuite/Changelog:

     * gdb.fortran/vla-history.exp: Lookup array elements and printing exceeds timeout.