gdb/testsuite: Reduce test name duplication in gdb.python tests

This commit removes some, but not all, of the test name duplication
within the gdb.python tests.  On my local machine this takes the
number of duplicate test names in this set of tests from 174 to 85.
It is possible that different setups might encounter more duplicate
tests.

gdb/testsuite/ChangeLog:

	* gdb.python/py-parameter.exp: Make test names unique.
	* gdb.python/py-template.exp: Likewise.
	* gdb.python/py-value.exp: Likewise.