Add a utility function to lldbtest.py to return the line number of a matched string

within a file.  This is to be used within the test case to avoid hardcoded line number.

array_types/TestArrayTypes.py is modified first to use this pattern.  Other test modules
to follow.

rdar://problem/8537816
Testsuite: don't set breakpoints by exact file & line number

llvm-svn: 116270