Merge bitcoin#12302: test: Make ua_comment test pass on 0.16.0

aac6bce test: Make ua_comment test pass on 0.16.0 (Wladimir J. van der Laan)

Pull request description:

  The specific length of the uacomment is one shorter on `0.16.0` than on `0.15.99` causing the (stupid) test to fail.

  This change makes `assert_start_raises_init_error` optionally take a regexp, so that the error message can be checked without being specific about the reported length.

Tree-SHA512: 1c5e9f1d0b36f004f8113c7e211e8281194ce8057869ac3702172d8b021df3c3aa3b8f79b9434678ed0fb7146f848802410647d434fc884aa200b6a5e26afe8b

test/functional/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 (287) 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")