fix(user): Use '*' as default password field rather than '!'

When using openssh without pam it checks for a ! prefix in the password
field, locking the account entirely if found. The other common lock
character, *, is allowed by ssh to login via ssh keys so use it instead.
fix(initialize): don't quote version or ID

The update_engine parsing and XML generation code is very naive. Instead
of trying to implement a correct parser and generater in C++ just
generate a file that doesn't have quote's around fields that we know
won't have spaces.
Merge pull request #64 from philips/no-quotes-on-oem-id-or-version

fix(initialize): don't quote version or ID
chore(release): Bump version to v0.4.0
chore(release): Bump version to v0.4.0+git
doc(oem): remove quotes from oem doc
fix(manage_etc_hosts): Append newline to /etc/hosts
Merge pull request #65 from bcwaldon/hosts-newline

fix(manage_etc_hosts): Append newline to /etc/hosts
Merge pull request #57 from marineam/passwd

fix(user): Use '*' as default password field rather than '!'
feat(units): Generic config drive and other systemd units.