Allow @TestCaseName to be for names that are compatible with CTS/AJUR

Previously, @TestCaseName was disallowed altogether and the default
format was set to {method}[{index}] which was compatible with CTS/AJUR.
The intent was to prevent test authors from setting names which would
break CTS/AJUR features such as retry.

This change relaxes the restrictions to allow the use of @TestCaseName
as long as the generated test names were compatible with CTS/AJUR, i.e.
consisted of what could be a method name followed by an optional index
in brackets.

e.g. {method}_{0} would be allowed as long as the first parameter to
the test contained characters that are allowed in an identifier. An
invalid test name is detected as soon as it is created and will cause
the test run to fail.

Bug: 36541809
Test: Tried using @TestCaseName with valid and invalid patterns
Change-Id: I1dbc99b6b181898b438997f3e6b6d79a60b212b6
diff --git a/README.google b/README.google
index 47541ba..a1ef97e 100644
--- a/README.google
+++ b/README.google
@@ -18,3 +18,6 @@
                  and prevent use of @TestCaseName.
                  Ignore tests broken by the above change.
       38419944 - Fix sharding on CTS.
+      36541809 - Partially revert 36541809 to allow @TestCaseName to be
+                 used as long as it generates a name that is compatible
+                 with CTS and AJUR.