ci: minor restructuring

use igwn/builder for building (S)RPMs, has a bunch of stuff pre-installed

.gitlab/ci/rhel.yml

@@ -12,15 +12,25 @@ include:
 
 # -- macros
 
-.el7:
-  image: igwn/base:el7-testing
+.el:
   variables:
     EPEL: "true"
 
+.el7:
+  extends: .el
+  image: igwn/base:el7-testing
+
+.el7-builder:
+  extends: .el7
+  image: igwn/builder:el7-testing
+
 .el8:
+  extends: .el
   image: igwn/base:el8-testing
-  variables:
-    EPEL: "true"
+
+.el8-builder:
+  extends: .el8
+  image: igwn/builder:el8-testing
 
 # -- source packages --------
 #
@@ -40,12 +50,12 @@ include:
 srpm:el7:
   extends:
     - .srpm
-    - .el7
+    - .el7-builder
 
 srpm:el8:
   extends:
     - .srpm
-    - .el8
+    - .el8-builder
 
 # -- binary packages --------
 #
@@ -64,14 +74,14 @@ srpm:el8:
 rpm:el7:
   extends:
     - .rpm
-    - .el7
+    - .el7-builder
   needs:
     - srpm:el7
 
 rpm:el8:
   extends:
     - .rpm
-    - .el8
+    - .el8-builder
   needs:
     - srpm:el8