The 'exec_file' will now try to check for the headers inside the file, in
case that it doesn't recognize the format or no format has been provided.
Also the processing part of the user data now checks if the 'Content-Type' is
in the file instead of checking if the file starts with the header, in
order to comply with RFC2045.
Change-Id: I53fda9f5c17f35cb35d93a86434ecc4c7c579802
Closes-Bug: #1623393
Closes-Bug: #1672222