In order to execute as root, the command string gets echo'd into so;
previusly, double quotes were used in echo, which caused any veriables
in the command string to be expanded _before_ it was echoed.
- adb protcol uses "\r\n" for line breaks. This is not handled by
Python's line break translation, as not a file. So spliting on '\n'
when extracting the exit code resulted in stray '\r' in the output.
- adb_shell expects exit code to be echoed on the same line. This may
not have been the case if latest output from executed command was not
a complete line. An extra echo will now ensure that the exit code will
be on its own line even in that case.
