Closes issue #261 on node_exporter. (#1403)

* Closes issue #261 on node_exporter.

Delegated mdstat parsing to procfs project. mdadm_linux.go now only exports the metrics.
-> Added disk labels: "fail", "spare", "active" to indicate disk status
-> hanged metric node_md_disks_total ==> node_md_disks_required
-> Removed test cases for mdadm_linux.go, as the functionality they tested for has been moved to procfs project.

Signed-off-by: Advait Bhatwadekar <advait123@ymail.com>

collector/fixtures/proc/mdstat

@@ -1,5 +1,6 @@
 Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
-md3 : active raid6 sda1[8] sdh1[7] sdg1[6] sdf1[5] sde1[11] sdd1[3] sdc1[10] sdb1[9]
+
+md3 : active raid6 sda1[8] sdh1[7] sdg1[6] sdf1[5] sde1[11] sdd1[3] sdc1[10] sdb1[9] sdd1[10](S) sdd2[11](S)
       5853468288 blocks super 1.2 level 6, 64k chunk, algorithm 2 [8/8] [UUUUUUUU]
 
 md127 : active raid1 sdi2[0] sdj2[1]
@@ -8,31 +9,31 @@ md127 : active raid1 sdi2[0] sdj2[1]
 md0 : active raid1 sdi1[0] sdj1[1]
       248896 blocks [2/2] [UU]
 
-md4 : inactive raid1 sda3[0] sdb3[1]
+md4 : inactive raid1 sda3[0](F) sdb3[1](S)
       4883648 blocks [2/2] [UU]
 
-md6 : active raid1 sdb2[2] sda2[0]
+md6 : active raid1 sdb2[2](F) sdc[1](S) sda2[0]
       195310144 blocks [2/1] [U_]
       [=>...................]  recovery =  8.5% (16775552/195310144) finish=17.0min speed=259783K/sec
 
-md8 : active raid1 sdb1[1] sda1[0]
-	  195310144 blocks [2/2] [UU]
-	  [=>...................]  resync =  8.5% (16775552/195310144) finish=17.0min speed=259783K/sec
+md8 : active raid1 sdb1[1] sda1[0] sdc[2](S) sde[3](S)
+      195310144 blocks [2/2] [UU]
+      [=>...................]  resync =  8.5% (16775552/195310144) finish=17.0min speed=259783K/sec
 
-md7 : active raid6 sdb1[0] sde1[3] sdd1[2] sdc1[1]
+md7 : active raid6 sdb1[0] sde1[3] sdd1[2] sdc1[1](F)
       7813735424 blocks super 1.2 level 6, 512k chunk, algorithm 2 [4/3] [U_UU]
       bitmap: 0/30 pages [0KB], 65536KB chunk
 
-md9 : active raid1 sdc2[2] sdd2[3] sdb2[1] sda2[0]
+md9 : active raid1 sdc2[2] sdd2[3] sdb2[1] sda2[0] sde[4](F) sdf[5](F) sdg[6](S)
       523968 blocks super 1.2 [4/4] [UUUU]
-	resync=DELAYED
+      resync=DELAYED
 
 md10 : active raid0 sda1[0] sdb1[1]
-      314159265 blocks 64k chunks
+       314159265 blocks 64k chunks
 
-md11 : active (auto-read-only) raid1 sdb2[0] sdc2[1]
+md11 : active (auto-read-only) raid1 sdb2[0] sdc2[1] sdc3[2](F) hda[4](S) ssdc2[3](S)
       4190208 blocks super 1.2 [2/2] [UU]
-	resync=PENDING
+      resync=PENDING
 
 md12 : active raid0 sdc2[0] sdd2[1]
       3886394368 blocks super 1.2 512k chunks
@@ -41,12 +42,15 @@ md126 : active raid0 sdb[1] sdc[0]
       1855870976 blocks super external:/md127/0 128k chunks
 
 md219 : inactive sdb[2](S) sdc[1](S) sda[0](S)
-    7932 blocks super external:imsm
+        7932 blocks super external:imsm
 
 md00 : active raid0 xvdb[0]
       4186624 blocks super 1.2 256k chunks
 
 md120 : active linear sda1[1] sdb1[0]
-      2095104 blocks super 1.2 0k rounding
+        2095104 blocks super 1.2 0k rounding
+
+md101 : active (read-only) raid0 sdb[2] sdd[1] sdc[0]
+      322560 blocks super 1.2 512k chunks
 
 unused devices: <none>

collector/fixtures/proc/mdstat_invalid

@@ -1,5 +0,0 @@
-Personalities : [invalid]
-md3 : invalid
-      314159265 blocks 64k chunks
-
-unused devices: <none>