Added SSH support to enable Git checkouts that use SSH instead of
HTTP(S).
The SSH directory is assumed to be in $HOME/.ssh; however:
export SSH_DIR=/my/custom/dir
will override the setting and allow for configurable settings.
$SSH_DIR is then mounted as host-volume in the Docker container and
placed in /home/<user>/.ssh
Backported from thewtex/docker-centos-build@26f7fd3
CentOS 5 is no longer supported and requests to obtain information from
the mirrors fails. However, the packages are still available on the
"Vault" mirrors.
Comment out the `mirrorlist` entries and set `enabled=0` in
CentOS-Base.repo, add entries for 5.11 in CentOS-Vault.repo and mark
them `enabled=1`.
While the use of sudo (made possible by 53cf084) allows to install
additional packages, the warning copied below was still reported.
To avoid this warning and streamline the installation of new packages,
this commit (1) introduces the concept of "pre_exec" entrypoint hook
and (2) adds such a hook to change the ownership of python "bin" and
"site-packages" directories for the manylinux images.
Warning reported are similar to this one:
```
The directory '/home/jcfr/.cache/pip/http' or its parent directory is
not owned by the current user and the cache has been disabled. Please
check the permissions and owner of that directory. If executing pip
with sudo, you may want sudo's -H flag.
```
Note that the sudo "-H" flag suggested in the warning is not available
in centos.
