python fix lint warnings

flake8 started to report warnings like this:
test/zdtm.py:1337:6: W605 invalid escape sequence '\S'
Signed-off-by: Andrei Vagin <avagin@gmail.com>

scripts/flake8.cfg

@@ -5,4 +5,5 @@
 # E251 unexpected spaces around keyword / parameter equals
 # E101 indentation contains mixed spaces and tabs
 # E126 continuation line over-indented for hanging indent 
-ignore = W191,E128,E501,E251,E101,E126
+# W504 line break after binary operator 
+ignore = W191,E128,E501,E251,E101,E126,W504

test/zdtm.py

@@ -122,7 +122,7 @@ def check_core_files():
 	if not reports:
 		return False
 
-	while subprocess.Popen("ps axf | grep 'abrt\.sh'", shell = True).wait() == 0:
+	while subprocess.Popen(r"ps axf | grep 'abrt\.sh'", shell = True).wait() == 0:
 		time.sleep(1)
 
 	for i in reports:
@@ -189,7 +189,7 @@ class ns_flavor:
 
 	def __copy_libs(self, binary):
 		ldd = subprocess.Popen(["ldd", binary], stdout = subprocess.PIPE)
-		xl = re.compile('^(linux-gate.so|linux-vdso(64)?.so|not a dynamic|.*\s*ldd\s)')
+		xl = re.compile(r'^(linux-gate.so|linux-vdso(64)?.so|not a dynamic|.*\s*ldd\s)')
 
 		# This Mayakovsky-style code gets list of libraries a binary
 		# needs minus vdso and gate .so-s
@@ -1334,7 +1334,7 @@ def get_visible_state(test):
 
 		cmounts = []
 		try:
-			r = re.compile("^\S+\s\S+\s\S+\s(\S+)\s(\S+)\s\S+\s[^-]*?(shared)?[^-]*?(master)?[^-]*?-")
+			r = re.compile(r"^\S+\s\S+\s\S+\s(\S+)\s(\S+)\s\S+\s[^-]*?(shared)?[^-]*?(master)?[^-]*?-")
 			with open("/proc/%s/root/proc/%s/mountinfo" % (test.getpid(), pid)) as mountinfo:
 				for m in mountinfo:
 					cmounts.append(r.match(m).groups())