Explicit install_user setting

[dokterbob]

Builds/unzips etc. are currently executed under the user who does the login.
As we work towards multi-user deploy this gives problems (e.g. Oleh makes a deploy and now the repo folders are owned by him). Instead, we could sudo to an explicit install user.

Concept:

• Common setting install_user and a single playbook to set up this user and a group for it.
• Role-specific settings, e.g. crawler_install_user.
• Playbooks set role-specific settings based on common settings.

Example of error:

TASK [services/crawler : clone ipfs-search] ***************************************************************************************************************************************
fatal: [booth]: FAILED! => {"changed": false, "msg": "Failed to set a new url https://github.com/ipfs-search/ipfs-search.git for origin:  fatal: detected dubious ownership in repository at '/tmp/ipfs-crawler'\nTo add an exception for this directory, call:\n\n\tgit config --global --add safe.directory /tmp/ipfs-crawler\n"}

drbob@booth:~$ ls -la /tmp/ipfs-crawler/
total 23532
drwxrwxr-x 12 oleh_p oleh_p     4096 Oct 28 22:50 .
drwxrwxrwt 19 root   root      28672 Nov  4 09:16 ..
-rw-rw-r--  1 oleh_p oleh_p      336 Oct 28 20:56 .codeclimate.yml
drwxrwxr-x  2 oleh_p oleh_p     4096 Oct 28 20:56 commands
[...]