Add Cirrus CI (#7431)

* Cirrus: Add Tox task

* Cirrus: Add Locale task

* Cirrus: Add Flake8 Task

* Cirrus: Add Regtest task

* Regtest: Flush stdout

Allows viewing output sooner.

* Regtest: Read process.stdout in text mode

Improves ability to quickly see output.

* Cirrus: Add Windows task

* Cirrus: Add Android task

* Cirrus: Add macOS task

* Cirrus: Add AppImage task

* Cirrus: Add tarball task

* Cirrus: Add Submodules task

* Android: remove superfluous cp/rm

* Add .dockerignore

Symlink to .gitignore.

contrib/android/Dockerfile

@@ -151,7 +151,7 @@ RUN chown ${USER} /opt
 USER ${USER}
 
 
-COPY requirements-build-android.txt /opt/deterministic-build/
+COPY contrib/deterministic-build/requirements-build-android.txt /opt/deterministic-build/
 RUN python3 -m pip install --no-dependencies --user \
     -r /opt/deterministic-build/requirements-build-android.txt
 

contrib/android/build.sh

@@ -22,12 +22,11 @@ if [ ! -z "$ELECBUILD_NOCACHE" ] ; then
 fi
 
 info "building docker image."
-cp "$CONTRIB/deterministic-build/requirements-build-android.txt" "$CONTRIB_ANDROID/requirements-build-android.txt"
 sudo docker build \
     $DOCKER_BUILD_FLAGS \
     -t electrum-android-builder-img \
-    "$CONTRIB_ANDROID"
-rm "$CONTRIB_ANDROID/requirements-build-android.txt"
+    --file "$CONTRIB_ANDROID/Dockerfile" \
+    "$PROJECT_ROOT"
 
 
 # maybe do fresh clone