I tried to run your docker image. Building went "fine", only the Webterminal step failed... so I commented this part for now.

RUN ccontrol start $ISC_PACKAGE_INSTANCENAME
RUN printf "SuperUser\n${ISC_PACKAGE_USER_PASSWORD}\n"
#RUN csession $ISC_PACKAGE_INSTANCENAME -U USER "##class(%SYSTEM.OBJ).Load(\"${TMP_INSTALL_DIR}/${WEBTERMINAL_DIST}\",\"cdk\")"

But I get an error as soon as I try to run the image...

C:\Dev\iris_db>docker run -p 57772:57772 -p 1972:1972 -e ROOT_PASS="linux" --name HSTEST hs2018:care -i=HEALTHSHARE
2019/08/28 13:10:53 Starting Caché...
2019/08/28 13:10:53 Seeked /usr/healthshare/mgr/cconsole.log - &{Offset:0 Whence:2}
2019/08/28 13:10:54 Error & possible causes:
2019/08/28 13:10:54 -Caché was not installed successfully
2019/08/28 13:10:54 -wrong Caché instance name
2019/08/28 13:10:54 -missing privileges to start/stop Caché; proc not in Caché group.
2019/08/28 13:10:54 ERR: exit status 1;
Now attempting WIJ compare, ./CACHE.WIJ

Cache Write Image File has blocks to be written, but it has an illegal format,
We failed to fully restore the WIJ. The recommended action is to
abort cstart, resolve the problem and try again. The other
option is you can delete the image journal and continue with cstart.
If you delete the image journal and continue you will probably have
database degradation in the databases that were not fully restored.

If you are not absolutely sure you want to do this, do not continue
if you change your mind, you can run cstart again and you will
be given this choice again.
Is an operator present to answer questions (Y/N)? Y =>
Do you want to delete the Write Image File (Y/N)? N =>
A problem was encountered while attempting to restore the write image
journal file (CACHE.WIJ). See the console log for more information
before attempting to start cache again.

** Startup aborted **

Starting HEALTHSHARE
Recovery failure. Startup aborted.

Note :  I've swiched to healthshare health connect 2018.1 instead...  and used the according cache.key.