sci-misc/boinc: Upgraded init script

sci-misc/boinc: Upgraded init script

Gentoo-Bug: 574260

After hot-fixing bug 574260, the following fixes/additions, suggested
by Jan Chren were made:

- #!/sbin/runscript -> #!/sbin/openrc-run
- Variables from /etc/conf.d/boinc are checked, and empty variables
  are pre-filled with sane defaults.
- split start() to start_pre() and start()
- removed check_baselayout()
- replaced /etc/init.d/boinc with ${RC_SERVICE}
- replaced echo with einfo ""
- replaced ${SVCNAME} with ${RC_SVCNAME}
- removed unset for local vars

Package-Manager: portage-2.2.28