remove duplicate logging and change logging levels of few loggings

[ZhuozhaoLi]

The changes in this PR:

1. Remove a duplicate logging line.
2. Change logging level of several lines from debug to info level, so that they won't slow down the interchange.

[benclifford]

This PR is failing CI because:

pytest-xdist 1.28.0 has requirement pytest>=4.4.0, but you'll have pytest 3.7.1 which is incompatible.

which is possibly because test-requirements.txt has a restriction on pytest versions, but not on pytest-xdist.

The version of pytest-xdist in my development virtualenv is 1.26.1

This probably means that a clean build from master will also fail, and it would be appropriate to have a separate PR to fix this problem - perhaps by pinning pytest-xdist to 1.26.1, because there is a reason that the version on pytest is pinned - see 4355ef8

[benclifford]

see #850 for a potential CI fix.

[yadudoc]

These change look good to go.