flake8 E741 variable name warning

Update the zts-report.py script to conform to the flake8 E741 rule.

    "Variables named I, O, and l can be very hard to read. This is
    because the letter I and the letter l are easily confused, and
    the letter O and the number 0 can be easily confused."

- https://www.flake8rules.com/rules/E741.html

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #10323

tests/test-runner/bin/zts-report.py

@@ -272,8 +272,8 @@ def process_results(pathname):
     pattern_log = r'^\s*Log directory:\s*(\S*)'
 
     d = {}
-    for l in f.readlines():
-        m = re.match(pattern, l)
+    for line in f.readlines():
+        m = re.match(pattern, line)
         if m and len(m.groups()) == 4:
             summary['total'] += 1
             if m.group(4) == "PASS":
@@ -281,7 +281,7 @@ def process_results(pathname):
             d[m.group(1)] = m.group(4)
             continue
 
-        m = re.match(pattern_log, l)
+        m = re.match(pattern_log, line)
         if m:
             summary['logfile'] = m.group(1)