get rid of hardcoded tomcat version from sw360empty/Dockerfile
get rid of hardcoded tomcat version from sw360empty/Dockerfile

Use shell form CMD to expand the $TOMCAT environment variable
configured in entrypoint.sh script.

Signed-off-by: Atsushi Nemoto <7e8cd96c99dfba553c3e0481a391e58645ecade6@sord.co.jp>

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