Ironic creates hardlinks between the TFTP master image store and the
HTTP root path when iPXE is enabled. With Docker volumes used for these
locations we run into https://bugs.launchpad.net/ironic/+bug/1507894
during deployment. If we use a directory under /httpboot to store the
master images this issue is avoided.
This change uses the new bifrost config variable,
ironic_tftp_master_path added in [1] to configure the path, rather than
the existing hacked approach of modifying the ironic.conf config file
after the bifrost_deploy container has started.
[1] https://review.openstack.org/#/c/577071
Change-Id: I5c62999c4956bebd0d3920d756ce67ba194b0ebe
e78f823110