Update for Docker: use the install-plugins.sh script. It takes a list of plugin names minus the '-plugin' extension. See the description here.
install-plugins.sh replaces the deprecated plugins.sh which now warns :
WARN: plugins.sh is deprecated, please switch to install-plugins.sh
To use a plugins.txt as per plugins.sh see this issue and this workaround:
RUN /usr/local/bin/install-plugins.sh $(cat /usr/share/jenkins/plugins.txt | tr '\n' ' ')