openshift.ks: Refactor high-level install steps

Factor the steps at the end of the script into a new configure_all
function, and call that function after parse_cmdline and set_defaults.

Modify the generation rules for generic/openshift.sh and
amazon/openshift-amz.sh to take this change into account.
openshift.ks: Rename parse_cmdline

Rename parse_cmdline to parse_kernel_cmdline.
openshift.ks: Refactor argument parsing

Factor the new function parse_args out of parse_kernel_cmdline.
openshift.ks: Add CONF_ACTIONS

Add the CONF_ACTIONS setting, using which the user can specify
a comma-separated list of functions to run.

Assign CONF_ACTIONS the value configure_all by default.

Don't run configure_all unconditionally.  Now the user can override the
default installation process to provide a list of steps to run or even
specify only one action to run, for example to reconfigure a single
service.