CI: add github workflow to run Coverity scans

Add a workflow that performs a build like it's done by osstest
Coverity flight and uploads the result to Coverity for analysis. The
build process is exactly the same as the one currently used in
osstest, and it's also run at the same time (bi-weekly).

This has one big benefit over using osstest: we no longer have to care
about keeping the Coverity tools up to date in osstest.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

.github/workflows/coverity.yml

@@ -0,0 +1,41 @@
+name: Coverity Scan
+
+# We only want to test official release code, not every pull request.
+on:
+  schedule:
+    - cron: '18 9 * * WED,SUN' # Bi-weekly at 9:18 UTC
+
+jobs:
+  coverity:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Install build dependencies
+      run: |
+        sudo apt-get install -y wget git bcc bin86 gawk bridge-utils \
+          iproute2 libcurl4-openssl-dev bzip2 libpci-dev build-essential \
+          make gcc libc6-dev libc6-dev-i386 linux-libc-dev zlib1g-dev \
+          libncurses5-dev patch libvncserver-dev libssl-dev libsdl-dev iasl \
+          libbz2-dev e2fslibs-dev git-core uuid-dev ocaml libx11-dev \
+          ocaml-findlib xz-utils libyajl-dev libpixman-1-dev \
+          libaio-dev libfdt-dev cabextract libglib2.0-dev autoconf automake \
+          libtool libfuse-dev liblzma-dev ninja-build \
+          kpartx python3-dev golang python-dev libsystemd-dev
+
+    - uses: actions/checkout@v2
+      with:
+        ref: staging
+
+    - name: Configure Xen
+      run: |
+        ./configure
+
+    - name: Pre build stuff
+      run: |
+        make -C tools/firmware/etherboot all && make mini-os-dir
+
+    - uses: vapier/coverity-scan-action@v1
+      with:
+        command: make xen tools && make -C extras/mini-os/
+        project: XenProject
+        email: ${{ secrets.COVERITY_SCAN_EMAIL }}
+        token: ${{ secrets.COVERITY_SCAN_TOKEN }}