Force a Gerrit change to be build on all four Android builders

[Stephan Bergmann]

Normally, Jenkins will build a Gerrit change on just two out of the four 
different Android build configurations, either arm and x86_64, or 
aarch64 and x86.  Occasionally, it might be beneficial to build a 
specific change on all four of them.  (For example, 
<https://gerrit.libreoffice.org/c/core/+/155346/> "external/hunspell: 
Work around missing C++20 std::bit_cast" fixes a gerrit_android_x86-only 
issue, so it wouldn't be helpful if Jenkins happened to not build it for 
that configuration.)

With the help of Cloph, I modified 
<https://ci.libreoffice.org/job/gerrit_master_android/> so that it will 
build a Gerrit change for all four configurations if the Gerrit change's 
topic 
(<https://gerrit-review.googlesource.com/Documentation/intro-user.html#topics>) 
is "android:all" (without the quotes).

(Ideally, this feature would use hashtags, 
<https://gerrit-review.googlesource.com/Documentation/intro-user.html#hashtags>, 
rather than topics, but that doesn't work because of 
<https://issues.jenkins.io/browse/JENKINS-55342> "Add hashtags support 
in Jenkins building parameters".)

(This is a master-only feature.  The Jenkins 7.5 and 7.6 branch 
configurations don't build Android at all.)