git-p4: fix instantiation of CalledProcessError

CalledProcessError is an exception class from the subprocess namespace.
When raising this exception, git-p4 would instantiate CalledProcessError
objects without properly referencing the subprocess namespace causing
the script to fail.

Resolves the issue by replacing CalledProcessError with
subprocess.CalledProcessError.

Signed-off-by: Joel Holdsworth <jholdsworth@nvidia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-p4.py b/git-p4.py
index 986595b..eefac27 100755
--- a/git-p4.py
+++ b/git-p4.py
@@ -394,7 +394,7 @@ def system(cmd, ignore_error=False):
         sys.stderr.write("executing %s\n" % str(cmd))
     retcode = subprocess.call(cmd, shell=expand)
     if retcode and not ignore_error:
-        raise CalledProcessError(retcode, cmd)
+        raise subprocess.CalledProcessError(retcode, cmd)
 
     return retcode
 
@@ -404,7 +404,7 @@ def p4_system(cmd):
     expand = not isinstance(real_cmd, list)
     retcode = subprocess.call(real_cmd, shell=expand)
     if retcode:
-        raise CalledProcessError(retcode, real_cmd)
+        raise subprocess.CalledProcessError(retcode, real_cmd)
 
 def die_bad_access(s):
     die("failure accessing depot: {0}".format(s.rstrip()))
@@ -4169,7 +4169,7 @@ def run(self, args):
             init_cmd.append("--bare")
         retcode = subprocess.call(init_cmd)
         if retcode:
-            raise CalledProcessError(retcode, init_cmd)
+            raise subprocess.CalledProcessError(retcode, init_cmd)
 
         if not P4Sync.run(self, depotPaths):
             return False