Deduplicate warnings&errors found in logs and add initial newline in output

It isn't useful to report duplicate errors multiple times. And e.g.
configure may report a wrong option at the start and end.
Hence deduplicate it.
Also change the logged warning/error to include a newline & tab in front
of each element which makes it nicer to read. E.g.:
> build failed (first 300 chars): Found 1 error(s) in command output:
>	configure: WARNING: unrecognized options: --with-foo, --with-bar (took 2 mins 39 secs)

Author: Flamefire

easybuild/tools/run.py

@@ -52,7 +52,7 @@
 from easybuild.tools.config import ERROR, IGNORE, WARN, build_option
 from easybuild.tools.hooks import RUN_SHELL_CMD, load_hooks, run_hook
 from easybuild.tools.py2vs3 import string_type
-from easybuild.tools.utilities import trace_msg
+from easybuild.tools.utilities import nub, trace_msg
 
 
 _log = fancylogger.getLogger('run', fname=False)
@@ -790,7 +790,7 @@ def extract_errors_from_log(log_txt, reg_exps):
                 elif action == WARN:
                     warnings.append(line)
                 break
-    return warnings, errors
+    return nub(warnings), nub(errors)
 
 
 def check_log_for_errors(log_txt, reg_exps):
@@ -805,8 +805,8 @@ def check_log_for_errors(log_txt, reg_exps):
 
     errors_found_in_log += len(warnings) + len(errors)
     if warnings:
-        _log.warning("Found %s potential error(s) in command output (output: %s)",
+        _log.warning("Found %s potential error(s) in command output:\n\t%s",
                      len(warnings), "\n\t".join(warnings))
     if errors:
-        raise EasyBuildError("Found %s error(s) in command output (output: %s)",
+        raise EasyBuildError("Found %s error(s) in command output:\n\t%s",
                              len(errors), "\n\t".join(errors))