tests/30-audio: Fix dd command, better pulseaudio test.

Incorrect dd direction might be causing the test to fail
occasionally (#1101).
Set UID_MIN to 1001 to make sure that useradd does not automatically add users with UID 1000.

This guarantees that UID 1000 is available when post-common adds the main user at the end of the first run of crouton.

Protect GID 1000 in the same way.

Fixes a bug when xbmc is selected during the Arch install (the xmbc user created by the package steals UID 1000).
arch: installer
arch: enter-chroot: source /etc/profile.

Workaround for bug in su/bash, where /etc/profile is not sourced,
even though su is called with '-' (login shell).
See: https://bugs.archlinux.org/task/31831
This is necessary to get /usr/local/bin in the PATH, and setup the
correct locale, among other things. This is not necessary in Ubuntu,
as these are set by /etc/pam.d/su
arch: core/post-common.
arch: x11/xephyr/x11-common
arch: targets: Most DE and X11-related targets.
arch: chrome-common
arch: kde
arch: gnome

/etc/X11/xinit/xinitrc has a different meaning in Arch, and is
just a default xinit file.
arch: extension: Add desktop file so it can be set as default browser.
arch: audio and tests/30-audio
arch: Do not rely on /etc/os-release anymore

ArchLinux removed it from filesystem package.
Fix xorg target on Xorg >=1.16

Configure Xorg.wrap back to its former behaviour (<1.16).
arch/unity: Blacklisted by other test already.
arch/chrome: Fix channels.