test: Make ua_comment test pass on 0.16.0

The specific length of the uacomment is one shorter on `0.16.0` than on
`0.15.99` causing the (stupid) test to fail.
Just match the latter part of the message only.

Author: laanwj

test/functional/feature_uacomment.py

@@ -23,7 +23,7 @@ def run_test(self):
 
         self.log.info("test -uacomment max length")
         self.stop_node(0)
-        expected = "Total length of network version string (286) exceeds maximum length (256). Reduce the number or size of uacomments."
+        expected = "exceeds maximum length (256). Reduce the number or size of uacomments."
         self.assert_start_raises_init_error(0, ["-uacomment=" + 'a' * 256], expected)
 
         self.log.info("test -uacomment unsafe characters")