isort: add black-friendly isort config

Nearly perfect match config to black formatting with one exception:
psf/black#251

That gap should be filled with the 'ensure_newline_before_comments=True'
that won't be honored until the next version of isort.

Signed-off-by: Chris Patterson <chris.patterson@canonical.com>

.isort.cfg

@@ -0,0 +1,7 @@
+[settings]
+multi_line_output=3
+include_trailing_comma=True
+force_grid_wrap=0
+use_parentheses=True
+line_length=88
+ensure_newline_before_comments=True