python-utils-r1.eclass: epytest, force color output to match NOCOLOR

Force pytest color output on or off based on the presence and value
of NOCOLOR envvar.  This fixes inconsistent use of colors that largely
depended on upstream pytest settings.

Signed-off-by: Michał Górny <mgorny@gentoo.org>

eclass/python-utils-r1.eclass

@@ -1297,6 +1297,16 @@ epytest() {
 
 	_python_check_EPYTHON
 
+	local color
+	case ${NOCOLOR} in
+		true|yes)
+			color=no
+			;;
+		*)
+			color=yes
+			;;
+	esac
+
 	local args=(
 		# verbose progress reporting and tracebacks
 		-vv
@@ -1308,6 +1318,8 @@ epytest() {
 		# override filterwarnings=error, we do not really want -Werror
 		# for end users, as it tends to fail on new warnings from deps
 		-Wdefault
+		# override color output
+		"--color=${color}"
 	)
 	local x
 	for x in "${EPYTEST_DESELECT[@]}"; do