Dockerfile improvement (#1017)

* build(dockerfile): support preinstalling custom solc

* build(dockerfile): run with normal user mythril

* build(dockerfile): fix install SOLC command & install under mythril user

* fix.build(dockerfile): when build-time argument SOLC not specified

* fix.build & chore(dockerfile): copy signature db to user directory & remove CHOWN operation for copied files

Fix copying to `signatures.db` to root home directory mistake. `chown` operation was unnecessary and removed.

Dockerfile

@@ -1,5 +1,8 @@
 FROM ubuntu:bionic
 
+# Space-separated version string without leading 'v' (e.g. "0.4.21 0.4.22") 
+ARG SOLC
+
 RUN apt-get update \
   && apt-get install -y \
      libsqlite3-0 \
@@ -36,5 +39,12 @@ COPY . /opt/mythril
 RUN cd /opt/mythril \
   && python setup.py install
 
-COPY ./mythril/support/assets/signatures.db /root/.mythril/signatures.db
+RUN useradd -m mythril
+USER mythril
+WORKDIR /home/mythril
+
+RUN ( [ ! -z "${SOLC}" ] && set -e && for ver in $SOLC; do python -m solc.install v${ver}; done ) || true
+
+COPY ./mythril/support/assets/signatures.db /home/mythril/.mythril/signatures.db
+
 ENTRYPOINT ["/usr/local/bin/myth"]