ci-workers: Variable overrides and process tweaks for CentOS 7

Part of #2510

contrib/ci-workers/vars/CentOS.yml

@@ -0,0 +1,13 @@
+---
+buildbot_deps: [] # Empty to remove python-pip
+build_deps:
+  - bzip2
+  - gcc
+  - gcc-c++
+  - make
+  - patch
+dist_deps:
+  - pkgconfig # Required until b556beda264308e040f8d88aca4f2f386a0183d9 is pulled in
+  - python-devel
+  - redhat-rpm-config
+pip_bin_dir: /usr/bin