Use the default branch for each SCM if no commit or branch is specified

Author: screamerbg

mbed/mbed.py

@@ -254,6 +254,7 @@ def _scm(cls):
 @staticclass
 class Bld(object):
     name = 'bld'
+    def_branch = 'default'
 
     def isurl(url):
         m_url = re.match(regex_url_ref, url.strip().replace('\\', '/'))
@@ -373,6 +374,7 @@ def getbranch():
 @staticclass
 class Hg(object):
     name = 'hg'
+    def_branch = 'default'
     ignore_file = os.path.join('.hg', 'hgignore')
 
     def isurl(url):
@@ -573,6 +575,7 @@ def unignore(dest):
 @staticclass
 class Git(object):
     name = 'git'
+    def_branch = 'master'
     ignore_file = os.path.join('.git', 'info', 'exclude')
 
     def isurl(url):
@@ -1078,6 +1081,8 @@ def clone(self, url, path, rev=None, depth=None, protocol=None, **kwargs):
                         scm.seturl(formaturl(url, protocol))
                         scm.cleanup()
                         info("Update cached copy from remote repository")
+                        if not rev:
+                            rev = scm.def_branch
                         scm.update(rev, True)
                         main = False
                 except (ProcessException, IOError):