e2e: fix tests

Use basic sleeps in busybox images. busybox are very light, and ping has
permissions complications, and it may fail for network related
issues.

e2e/scheduler_sysbatch/input/sysbatch_dispatch.nomad

@@ -20,10 +20,10 @@ job "sysbatchjob" {
       driver = "docker"
 
       config {
-        image = "bash:5"
+        image = "busybox:1"
 
-        command = "bash"
-        args    = ["-c", "ping -c 10 example.com"]
+        command = "/bin/sh"
+        args    = ["-c", "echo hi; sleep 1"]
       }
     }
   }

e2e/scheduler_sysbatch/input/sysbatch_job_fast.nomad

@@ -15,10 +15,10 @@ job "sysbatchjob" {
       driver = "docker"
 
       config {
-        image = "bash:5"
+        image = "busybox:1"
 
-        command = "bash"
-        args    = ["-c", "ping -c 10 example.com"]
+        command = "/bin/sh"
+        args    = ["-c", "echo hi; sleep 1"]
       }
     }
   }

e2e/scheduler_sysbatch/input/sysbatch_job_slow.nomad

@@ -15,10 +15,10 @@ job "sysbatchjob" {
       driver = "docker"
 
       config {
-        image = "bash:5"
+        image = "busybox:1"
 
-        command = "bash"
-        args    = ["-c", "ping -c 100000 example.com"]
+        command = "/bin/sh"
+        args    = ["-c", "echo hi; sleep 1000000"]
       }
     }
   }

e2e/scheduler_sysbatch/input/sysbatch_periodic.nomad

@@ -20,10 +20,10 @@ job "sysbatchjob" {
       driver = "docker"
 
       config {
-        image = "bash:5"
+        image = "busybox:1"
 
-        command = "bash"
-        args    = ["-c", "ping -c 10 example.com"]
+        command = "/bin/sh"
+        args    = ["-c", "echo hi; sleep 1"]
       }
     }
   }

e2e/scheduler_system/input/system_job0.nomad

@@ -23,9 +23,9 @@ job "system_job" {
       driver = "docker"
 
       config {
-        image = "bash:latest"
+        image = "busybox:1"
 
-        command = "bash"
+        command = "/bin/sh"
         args    = ["-c", "sleep 15000"]
       }
 

e2e/scheduler_system/input/system_job1.nomad

@@ -23,9 +23,9 @@ job "system_job" {
       driver = "docker"
 
       config {
-        image = "bash:latest"
+        image = "busybox:1"
 
-        command = "bash"
+        command = "/bin/sh"
         args    = ["-c", "sleep 15000"]
       }