ci: Add a job testing with rhg installed as `hg`

This significantly increases test coverage of rhg, without duplicating
many tests that already exist.

The `cargo build` command being remove only compiled a `rhg` executable
(as shown by the preceding `cd` command) but since a previous patch
`run-tests.py --rhg` now takes care of that.

Differential Revision: https://phab.mercurial-scm.org/D10196

contrib/heptapod-ci.yml

@@ -26,17 +26,6 b' variables:'
         - echo "$RUNTEST_ARGS"
         - HGTESTS_ALLOW_NETIO="$TEST_HGTESTS_ALLOW_NETIO" HGMODULEPOLICY="$TEST_HGMODULEPOLICY" "$PYTHON" tests/run-tests.py --color=always $RUNTEST_ARGS
 
-
-.rust_template: &rust
-    before_script:
-      - hg clone . /tmp/mercurial-ci/ --noupdate --config phases.publish=no
-      - hg -R /tmp/mercurial-ci/ update `hg log --rev '.' --template '{node}'`
-      - ls -1 tests/test-check-*.* > /tmp/check-tests.txt
-      - cd /tmp/mercurial-ci/rust/rhg
-      - cargo build --release
-      - cd /tmp/mercurial-ci/
-
-
 checks-py2:
     <<: *runtests
     variables:
@@ -95,7 +84,6 b' test-py3-pure:'
 
 test-py2-rust:
     <<: *runtests
-    <<: *rust
     variables:
         HGWITHRUSTEXT: cpython
         RUNTEST_ARGS: "--rust --blacklist /tmp/check-tests.txt"
@@ -103,13 +91,20 b' test-py2-rust:'
 
 test-py3-rust:
     <<: *runtests
-    <<: *rust
     variables:
         HGWITHRUSTEXT: cpython
         RUNTEST_ARGS: "--rust --blacklist /tmp/check-tests.txt"
         PYTHON: python3
         TEST_HGMODULEPOLICY: "rust+c"
 
+test-py3-rhg:
+    <<: *runtests
+    variables:
+        HGWITHRUSTEXT: cpython
+        RUNTEST_ARGS: "--rust --rhg --blacklist /tmp/check-tests.txt"
+        PYTHON: python3
+        TEST_HGMODULEPOLICY: "rust+c"
+
 test-py2-chg:
     <<: *runtests
     variables: