Use a try/except while executing this external command

So it catches things like FileNotFoundError
Signed-off-by: Mattia Rizzolo <mattia@debian.org>

managetests/branches.py

@@ -161,7 +161,7 @@ class Branch:
     def exec_command(self, raw_command, replaces=None, build=False):
         """Exec a command in the context of the branch"""
         args, kwargs = self.command_popen_args(raw_command, replaces, build)
-        return subprocess.call(*args, **kwargs) == 0
+        return subprocess.check_call(*args, **kwargs)
 
     def command_popen_args(self, raw_command, replaces=None, build=False):
         """Get the Popen arguments for exec_command"""
@@ -256,8 +256,11 @@ class Branch:
 
         # Build the website
         for cmd in self.config["build"]:
-            if not self.exec_command(cmd, build=True):
+            try:
+                self.exec_command(cmd, build=True)
+            except (IOError, subprocess.CalledProcessError) as e:
                 log("[!] Failed to execute build command: %s" % " ".join(cmd))
+                log("[!] Error: %s" % e)
                 log("[!] Aborting!")
                 self.fail_deployment(branch)