[beta] Move channel name to the end of the version string

This changes the version names on dev and beta from x.y.z-dev.m.n to
x.y.z-m.n.(dev|beta).

dart-lang/sdk#41535

Change-Id: I890c38c14edf059447eb1f82afcf9da468911d6b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143585
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: William Hesse <whesse@google.com>
Auto-Submit: Alexander Thomas <athom@google.com>

Author: athomas

tools/utils.py

@@ -379,7 +379,8 @@ def GetSemanticSDKVersion(no_git_hash=False, version_file=None):
     if version.channel == 'be':
         postfix = '-edge' if no_git_hash else '-edge.%s' % GetGitRevision()
     elif version.channel in ('beta', 'dev'):
-        postfix = '-dev.%s.%s' % (version.prerelease, version.prerelease_patch)
+        postfix = '-%s.%s.%s' % (version.prerelease, version.prerelease_patch,
+                                 version.channel)
     else:
         assert version.channel == 'stable'
         postfix = ''