patman: Move capture_sys_output() into terminal and rename

This function is sometimes useful outside tests. Also it can affect how
terminal output is done, e.g. whether ANSI characters should be emitted
or not.

Move it out of the test_util package and into terminal.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/elf_test.py b/tools/binman/elf_test.py
index 2f22639..5b17339 100644
--- a/tools/binman/elf_test.py
+++ b/tools/binman/elf_test.py
@@ -13,6 +13,7 @@
 
 from binman import elf
 from u_boot_pylib import command
+from u_boot_pylib import terminal
 from u_boot_pylib import test_util
 from u_boot_pylib import tools
 from u_boot_pylib import tout
@@ -187,7 +188,7 @@
             entry = FakeEntry(24)
             section = FakeSection()
             elf_fname = self.ElfTestFile('u_boot_binman_syms')
-            with test_util.capture_sys_output() as (stdout, stderr):
+            with terminal.capture() as (stdout, stderr):
                 elf.LookupAndWriteSymbols(elf_fname, entry, section)
             self.assertTrue(len(stdout.getvalue()) > 0)
         finally: