runqemu-gen-tapdevs: Allow run --help without sudo

runqemu-gen-tapdevs: Allow run --help without sudo

Then we can get user's UID and GID rather than hardcode to 1000, e.g.:

- Without sudo
$ runqemu-gen-tapdevs --help
[snip]
$ sudo ../poky/scripts/runqemu-gen-tapdevs 15220 100 4 tmp/sysroots-components/x86_64/qemu-helper-native/usr/bin
[snip]

- With sudo
$ sudo ../poky/scripts/runqemu-gen-tapdevs --help
[snip]
$ sudo ../poky/scripts/runqemu-gen-tapdevs 15220 100 4 tmp/sysroots-components/x86_64/qemu-helper-native/usr/bin
[snip]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>