Android, FFmpeg: Require patchelf 0.17.2 for shared builds

When building FFmpeg as shared libraries for Android, we rely on
patchelf to fix up the library dependencies. patchelf 0.18.0 is known
to produce broken Android binaries, which is why install-patchelf.sh
installs 0.17.2. However, nothing verified this, and
fix_ffmpeg_dependencies.sh only prints a warning for 0.18.0.

This patch makes install-ffmpeg-android.sh check that patchelf is
available and that its version is exactly 0.17.2.

Pick-to: 6.12
Change-Id: Ic9da3bcf5ac1a93b32def16b868e4d4d2ebc8f26
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>