Handled failure of execvp and increases am timeout.

The run_command_always() call fork and runs the command in the child
code, and user to have the above logic:

    if (pid == 0) {
        // boiling code
        execvp(command, (char**) args);
        // execvp's result will be handled after waitpid_with_timeout() below...
        _exit(-1); // ...but it doesn't hurt to force exit, just in case
    }

Recently, the _exit(-1) line was removed and there's been reports of
dumpstate hanging after, because it tries to wait for pid 0 to
finish (and in some cases it even tries to kill it).

Also increased the timeout when running am to send broadcasts.

BUG: 27804637
BUG: 27809534
Change-Id: Ia129253e367e5886d305947e56a643fd660a33bd