install-buildtools: fail if an error occurs

Several failure paths were displaying an error message but not returning,
so the install process continued and failed further.

(From OE-Core rev: b00e28735b64a781707441ec6187dd7f9240d97a)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/install-buildtools

@@ -258,6 +258,7 @@ def main():
             else:
                 logger.error("Checksum %s expected. Actual checksum is %s." %
                              (checksum, checksum_value))
+                return 1
 
         # Make installer executable
         logger.info("Making installer executable")
@@ -273,6 +274,7 @@ def main():
             ret = subprocess.call("%s -y" % tmpbuildtools, shell=True)
         if ret != 0:
             logger.error("Could not run buildtools installer")
+            return ret
 
         # Setup the environment
         logger.info("Setting up the environment")