Fixed a bug where drive names were calculated badly

This could result in situations where for example there was a single drive
named 'Drive2'. The user can then not create any more drives because the
nexts drive name would be 'Drive2' (because the calculation is just drive
count + 1). Now we just look for the first available name

pISO/src/newdrive.rs

@@ -425,9 +425,7 @@ impl input::Input for DriveFormat {
                     return Ok((false, vec![]));
                 }
                 _ => {
-                    let count = self.vg.volumes()?.len() + 1;
-
-                    let name = format!("Drive{}", count);
+                    let name = utils::next_available_drive_name(&self.vg)?;
                     let mut volume = self.vg.create_volume(&name, self.size)?;
 
                     DriveFormat::format_volume(&mut volume, &self.selected, &name)?;

pISO/src/utils.rs

@@ -1,4 +1,5 @@
-use error::{Result, ResultExt};
+use lvm;
+use error::{ErrorKind, Result, ResultExt};
 use std::ffi::OsStr;
 use std::fmt::Debug;
 use std::process::Command;
@@ -44,3 +45,13 @@ where
     }
     Err(format!("timeout while waiting for {}", path.as_ref().display()).into())
 }
+
+pub fn next_available_drive_name(vg: &lvm::VolumeGroup) -> Result<String> {
+    let volumes = vg.volumes()?;
+    for num in 1.. {
+        if volumes.iter().all(|vol| vol.name != format!("Drive{}", num)) {
+            return Ok(format!("Drive{}", num))
+        }
+    }
+    Err(ErrorKind::Msg("Failed to find valid drive number".into()).into())
+}