[LibOS/tests] Fix timing issues on certain LTP tests

- epoll01:          300 s -> skip
- pipe:              30 s -> 60 s
- clock_gettime04: disable test 1

Signed-off-by: Wojtek Porczyk <woju@invisiblethingslab.com>

libos/test/ltp/ltp.cfg

@@ -157,6 +157,16 @@ skip = yes
 [clock_gettime03]
 skip = yes
 
+# test #1 calls __vdso__clock_gettime(CLOCK_REALTIME) and checks if the
+# difference is <= 5 ms, which it might not be on a VM
+[clock_gettime04]
+must-pass =
+ 2
+ 3
+ 4
+ 5
+ 6
+
 # test 10: EOPNOTSUPP expected on CLOCK_THREAD_CPUTIME_ID
 [clock_nanosleep01]
 timeout = 40
@@ -247,9 +257,9 @@ skip = yes
 [dirtyc0w]
 skip = yes
 
-# very long test, does thousands of forks
+# very long test, does thousands of forks, unreliable
 [epoll01]
-timeout = 600
+skip = yes
 
 # tries to open /proc/1/stat, which is not implemented in Gramine
 [epoll_pwait01]
@@ -1373,6 +1383,9 @@ skip = yes
 [pipe03]
 skip = yes
 
+[pipe04]
+timeout = 60
+
 [pipe07]
 skip = yes