Demote package-is-already-installed log message to debug-level.
Demote package-is-already-installed log message to debug-level.

An info-level message for each package might be too intense. And it might give a false sense of security as well: it doesn't confirm that the virtualenv is non-empty; it merely notices when a package we're installing is already there.

xavfernandez/pip,zvezdan/pip,benesch/pip,pfmoore/pip,willingc/pip,natefoo/pip,fiber-space/pip,esc/pip,sigmavirus24/pip,fiber-space/pip,techtonik/pip,esc/pip,rbtcollins/pip,techtonik/pip,RonnyPfannschmidt/pip,alex/pip,willingc/pip,atdaemon/pip,sbidoul/pip,mindw/pip,rouge8/pip,pradyunsg/pip,zvezdan/pip,dstufft/pip,RonnyPfannschmidt/pip,xavfernandez/pip,benesch/pip,zvezdan/pip,ncoghlan/pip,dstufft/pip,esc/pip,atdaemon/pip,sbidoul/pip,alex/pip,dstufft/pip,sigmavirus24/pip,rouge8/pip,jythontools/pip,mindw/pip,alex/pip,pypa/pip,natefoo/pip,xavfernandez/pip,pfmoore/pip,mindw/pip,techtonik/pip,ncoghlan/pip,RonnyPfannschmidt/pip,pypa/pip,rouge8/pip,jythontools/pip,jythontools/pip,rbtcollins/pip,rbtcollins/pip,natefoo/pip,benesch/pip,pradyunsg/pip,nthall/pip,atdaemon/pip,sigmavirus24/pip,nthall/pip,fiber-space/pip,willingc/pip,nthall/pip,ncoghlan/pip