file: extend exec acl checks to commands with arguments

file: extend exec acl checks to commands with arguments

When the initial exec permission check on the executable path fails,
concatenate the command line with spaces and use the resulting string
as lookup path for a second exec permission check.

This allows for exec acls similar to this example:

    "file": {
        "/usr/bin/program --flag --option=1 arg *": [ "exec" ]
    }

The example above would allow executing `/usr/bin/program` with the
arguments `--flag`, `--option=1` and `arg` in exactly this order,
followed by any number of optional arguments as denoted by the
asterisk.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>