patch 8.1.1483: skipped tests are not properly listed

Problem:    Skipped tests are not properly listed.
Solution:   Throw a "Skipped" exception instead of using ":finish" or ":return".

Author: brammool

src/testdir/test_balloon.vim

@@ -9,7 +9,7 @@ if !has('gui_running')
 
 source screendump.vim
 if !CanRunVimInTerminal()
-  throw 'Skipped: cannot run Vim in a terminal window'
+  throw 'Skipped: cannot make screendumps'
 endif
 
 let s:common_script =<< [CODE]

src/testdir/test_breakindent.vim

@@ -5,7 +5,7 @@
 " It helps to change the tabstop setting and force a redraw (e.g. see
 " Test_breakindent08())
 if !exists('+breakindent')
-  finish
+  throw 'Skipped: breakindent option not supported'
 endif
 
 source view_util.vim

src/testdir/test_cdo.vim

@@ -1,7 +1,7 @@
 " Tests for the :cdo, :cfdo, :ldo and :lfdo commands
 
 if !has('quickfix')
-  finish
+  throw 'Skipped: quickfix feature missing'
 endif
 
 " Create the files used by the tests

src/testdir/test_channel.vim

@@ -1,15 +1,15 @@
 " Test for channel functions.
 
 if !has('channel')
-  finish
+  throw 'Skipped: channel feature missing'
 endif
 
 source shared.vim
 
 let s:python = PythonProg()
 if s:python == ''
   " Can't run this test without Python.
-  finish
+  throw 'Skipped: Python command missing'
 endif
 
 " Uncomment the next line to see what happens. Output is in

src/testdir/test_clientserver.vim

@@ -1,7 +1,7 @@
 " Tests for the +clientserver feature.
 
 if !has('job') || !has('clientserver')
-  finish
+  throw 'Skipped: job and/or clientserver feature missing'
 endif
 
 source shared.vim

src/testdir/test_conceal.vim

@@ -2,12 +2,12 @@
 " Also see test88.in (should be converted to a test function here).
 
 if !has('conceal')
-  finish
+  throw 'Skipped: conceal feature missing'
 endif
 
 source screendump.vim
 if !CanRunVimInTerminal()
-  finish
+  throw 'Skipped: cannot make screendumps'
 endif
 
 func Test_conceal_two_windows()

src/testdir/test_debugger.vim

@@ -22,7 +22,7 @@ endfunc
 " Debugger tests
 func Test_Debugger()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
 
   " Create a Vim script with some functions

src/testdir/test_diffmode.vim

@@ -748,7 +748,7 @@ endfunc
 
 func Test_diff_screen()
   if !CanRunVimInTerminal() || !has('menu')
-    return
+    throw 'Skipped: cannot make screendumps and/or menu feature missing'
   endif
   " clean up already existing swap files, just in case
   call delete('.Xfile1.swp')
@@ -880,7 +880,7 @@ endfunc
 
 func Test_diff_with_cursorline()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
 
   call writefile([
@@ -907,7 +907,7 @@ endfunc
 
 func Test_diff_of_diff()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
 
   call writefile([

src/testdir/test_fold.vim

@@ -708,7 +708,7 @@ endfunc
 
 func Test_folds_with_rnu()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([

src/testdir/test_highlight.vim

@@ -533,7 +533,7 @@ endfunc
 
 func Test_cursorline_after_yank()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([
@@ -555,7 +555,7 @@ endfunc
 
 func Test_cursorline_with_visualmode()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([
@@ -575,7 +575,7 @@ endfunc
 
 func Test_wincolor()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([