Fix grass-session installation in docker files (#517)

Due to https://github.com/zarch/grass-session/issues/16 all docker builds are currently broken.
This workaround pins the last working version by applying the workaround used in https://github.com/OSGeo/grass/pull/516

To be removed once `grass-session` is back functional.

docker/alpine/Dockerfile_alpine_latest

@@ -195,7 +195,10 @@ ENV INTEL="" \
 # =====================
 
 # install external Python API
-RUN pip install grass-session
+#RUN pip install grass-session
+# ugly workaround for https://github.com/zarch/grass-session/issues/16
+RUN apk add git
+RUN pip3 install --upgrade pip six git+git://github.com/zarch/grass-session.git@0b8414c1
 
 # set GRASSBIN
 ENV GRASSBIN="/usr/local/bin/grass"

docker/alpine/Dockerfile_alpine_wxgui

@@ -207,7 +207,10 @@ ENV INTEL="" \
 # =====================
 
 # install external Python API
-RUN pip install grass-session
+#RUN pip install grass-session
+# ugly workaround for https://github.com/zarch/grass-session/issues/16
+RUN apk add git
+RUN pip3 install --upgrade pip six git+git://github.com/zarch/grass-session.git@0b8414c1
 
 # set GRASSBIN
 ENV GRASSBIN="/usr/local/bin/grass"

docker/debian/Dockerfile_debian_pdal

@@ -225,7 +225,10 @@ RUN apt-get clean -y
 WORKDIR /scripts
 
 # install external GRASS GIS session Python API
-RUN pip3 install grass-session
+#RUN pip3 install grass-session
+# ugly workaround for https://github.com/zarch/grass-session/issues/16
+RUN apt-get install git
+RUN pip3 install --upgrade pip3 git+git://github.com/zarch/grass-session.git@0b8414c1
 
 # install GRASS GIS extensions
 RUN grass --tmp-location EPSG:4326 --exec g.extension extension=r.in.pdal

docker/ubuntu/Dockerfile_ubuntu_latest_pdal

@@ -171,7 +171,10 @@ RUN apt-get clean -y
 WORKDIR /scripts
 
 # install external GRASS GIS session Python API
-RUN pip3 install grass-session
+#RUN pip3 install grass-session
+# ugly workaround for https://github.com/zarch/grass-session/issues/16
+RUN apt-get install git
+RUN pip3 install --upgrade pip3 git+git://github.com/zarch/grass-session.git@0b8414c1
 
 # install GRASS GIS extensions
 RUN grass --tmp-location EPSG:4326 --exec g.extension extension=r.in.pdal

docker/ubuntu/Dockerfile_ubuntu_pdal

@@ -226,7 +226,10 @@ RUN apt-get clean -y
 WORKDIR /scripts
 
 # install external GRASS GIS session Python API
-RUN pip3 install grass-session
+#RUN pip3 install grass-session
+# ugly workaround for https://github.com/zarch/grass-session/issues/16
+RUN apt-get install git
+RUN pip3 install --upgrade pip3 git+git://github.com/zarch/grass-session.git@0b8414c1
 
 # install GRASS GIS extensions
 RUN grass --tmp-location EPSG:4326 --exec g.extension extension=r.in.pdal